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Currently, substantial efforts are being made in the aerospace industry to develop reusable launch vehicles (RLVs) insofar as the same are believed to be the next generation of space vehicles for deploying space exploration payloads into the next century. Ideally, such RLVs will be single-stage-to-orbit vehicles that are intended to be cheaper and easier to operate than current space vehicles.
One key factor that necessarily must be addressed in the development of such RLVs is weight reduction of the spacecraft. In this respect, it is recognized that reducing weight is a key factor in launching a payload into orbit, especially via a single-stage rocket.
Among the materials ideally suited for such applications comprise certain composite materials, and in particular composite materials formed from organic matrix materials and various filaments to form strong structures. Not only are such materials exceptionally lighter than other materials typically deployed in such applications, such as aluminum, but further have been shown to withstand the combined thermal and mechanical loads experienced by spacecraft during launch, orbit and reentry.
Such composite materials are further particularly well-suited for use in the construction of cryogenic fuel tanks that will necessarily be utilized as part of such RLVs. However, the fabrication of such cryogenic fuel tanks from such composite materials is problematic insofar as tanks constructed according to conventional manufacturing techniques fail to successfully survive flight operating conditions. In particular, such tanks are prone to fail at specific joints and seams formed therein at the juncture between the various composite skin components utilized to fabricate such tanks. In this regard, there have yet to be developed structural joints and seals for use in such tank structures that enable such structures to retain the structural durability necessary to withstand the thermal and mechanical loads encountered during space flight while at the same time minimizing weight attributable thereto and providing the necessary sealing. Indeed, permeability of composite materials has been a concern for engineers for some time, particularly with respect to the possibility that such materials can leak hydrogen.
Accordingly, there is a substantial need in the art for improved structural joints and seals for use in pressurized tank structures, and in particular cryogenic fuel tanks, that enable such tanks to be fabricated from such lightweight composite materials but yet possess the structural curability to enable the same to be repeatedly utilized in space flight. There is additionally a need in the art for structural joints and seals that, in addition to minimizing weight, are of simple construction and may be readily and easily deployed for use in a variety of applications. Still further, there is a need for structural joints and seals that can be utilized in any of a variety of applications specific to tank structures, and in particular, splice joint seals, frame seals and access cover openings.
The present invention specifically addresses and alleviates the above-identified deficiencies in the art. In this regard, the present invention is directed to novel structural joints and seals for use in pressurized structures, and in particular cryogenic fuel tanks formed from composite materials. According to a preferred embodiment, the structural joints and seals comprise a strain-compliant material as applied to a joint or seam to thus provide a surface to bridge such joint or seam with a continuous component skin to thus produce a completely bonded inner surface. The strain-compliant materials are further shaped to resist shear and peel stresses, as well as serve to act as a redundant leak barrier. Preferably, the strain-compliant material consists of reinforced plastic or metallic honeycomb, although foam core and homogeneous elastomeric materials may be utilized in certain applications.
Among the specific applications by which the structural joints and seals of the present application may be utilized are in connection with structural joints, namely, splice joint seals, frame seals and access cover openings of pressurized tank structures. In this respect, the structural joints and seals of the present invention permit construction of tanks from component skin and internal structural details using conventional aircraft joint construction techniques. It is further believed that such structural joints and seals are particularly well-suited for cryogenic fuel tanks, in addition to conventional non-cryogenic tanks containing liquids and gases.
It is therefore an object of the present invention to provide structural joints and seams and methods of fabricating the same that are useful in the manufacture of tanks for containing pressurized gases and liquids as formed from component skin that are exceptionally durable and can be utilized to seal joints and seams in a more durable and reliable manner than prior art devices and techniques.
Another object of the present invention is to provide structural joints and seams and methods of fabricating the same that serve to form a redundant leak barrier about a joint or seam as formed within a tank for receiving, holding and controllably releasing pressurized fluid and/or gas.
Another object of the present invention is to provide structural joints and seams and methods of fabricating the same that permit the construction of tanks for holding pressurized liquids and/or gases, and in particular cryogenic fuel tanks, from component skin using conventional aircraft joint construction techniques.
Still further objects of the present invention are to provide structural joints and seams and methods of fabricating the same that can be easily and readily fabricated from existing, commercially-available materials, can be utilized to form tanks that are exceptionally reliable, allows for the fabrication of cryogenic fuel tanks from composite skin materials that further enables such fuel tanks to be lighter weight but of equal or greater durability than prior art tanks, and may likewise be utilized for virtually all conventional, non-cryogenic tanks containing pressurized liquids and gases.